Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 14, 2025 ...

For a winter project I am helping my daughter to convert the old family Ford Excursion into a boondocking capable camper. Goal is no propane and no generator. We want to put in a B2B charging system to charge the house battery while driving, and also provide supplemental power with engine idling for cooking, etc.

There are some really good high efficiency and low cost inverters and smart chargers available and - being an experimenter - I decided to see if these could be combined to make a homemade B2B charger. Also, putting together a custom B2B system allows creating charge capacities that may not be available from B2B suppliers.

The B2B charger is activated by the VSR (voltage sensing relay) only with the engine running so no battery isolator is needed to protect the truck battery from discharge. To handle the extra load we upgraded the stock 130 amp alternator to a 220 amp alternator.

IOTA offers chargers with AGM and Lithium smart charge controllers in sizes from 30 amps to 90 amps.

AIMS and Spartan offer reasonably priced SW inverters. I have been working with Inverters-R-Us for advice and questions - highly recommended.

For our "prototype" system we are testing a 1000 watt Spartan inverter with the IOTA 30 amp charger with AGM charge controller to charge the 200 AH AGM house batteries for the truck camper.

This concept can easily be scaled up to 90 amps with readily available inverters and chargers. I would recommend planning for adding approximately 2X the amperage load on the alternator for some margin in hot weather, so for example with the 75 amp B2B size the alternator for 150 amps additional alternator load.

Here are some links from my research for examples
(I have no financial connection to these companies or products)

30 amp B2B - what we are currently testing
140 amp VSR
Amazon.com: 12V 140 Amp Dual Battery Smart Isolator by KeyLine - VSR -...
30 amp IOTA charger
DLS 30A Converter and Charger - 30 Amp ACDC Power Converter and Battery...
1000 watt Spartan inverter
Spartan Power 1000 Watt 12V Pure Sine Wave Inverter SP-PS1000

75 amp B2B
75 amp IOTA charger
DLS 75A Converter and Charger - 75 Amp ACDC Power Converter and Battery...
2000 watt Spartan inverter
Spartan Power 2000 Watt 12V Pure Sine Wave Inverter SP-PS2000

90 amp B2B
90 amp IOTA charger
DLS 90A Converter and Charger - 90 Amp ACDC Power Converter and Battery...
3000 watt AIMS inverter
Aims PWRI300012120SUL 3000 Watt 12V Pure Sine Wave Inverter

IOTA AGM and LIFEPO charge controllers

IQ4 AGM Smart Charge Controller
IQ4 AGM Smart Charge Controller - 3-Stage Smart Charge Controller for the...

IQ4 LIFEPO Smart Charge Controller
IQ4 LIFEPO Smart Charge Controller - 2-Stage Smart Charge Controller for the...

Homemade B2B Block Diagram


Underhood Inverter Installation


Underhood VSR Installation


Inverter Remote Installation


B2B Load Testing Bench
(daughter requires capability to run individually - microwave, induction hot plate, toaster, coffee maker)


200AH House Batteries